Ballast transformer with heat dissipating device

ABSTRACT

Ballast transformer is arranged in a housing with its coils resting on a spring bracket in contact with the housing so that heat from the coils is transmitted by the bracket to the housing for dissipation thereby.

United States atent [191 1111 3,883,834 Osteen' 1 May 13, 1975 1 BALLASTTRANSFORMER WITH HEAT 1,335,803 4/1920 Thardarson.... 336/92 DISSIPATINGDEVICE 2,282,040 5/1942 Doran 336/92 X 2,905,742 9/1959 Woods 174/35 TS[75] Inventor: Carl. M- Oste oma, N.C. 3,427,577 ,2/1969 Denes 336/61Assignee: General Electric p y 3,428,928 2/1969 Maines 336/61 7Pittsfield, Mass. 2 Filed; Dec. 13, 7 Primary ExaminerThomas J. KozmaAttorney, Agent, or Firm-Sidney Gr'eenburg [21] Appl, No.: 424,559

[52] US. Cl. 336/61; l74/DlG. 5; 336/92 57 T C [51] Int. Cl. HOlf 27/08[58] Field of Search 336/61, 90, 92, 100; Ballast transformer isarranged in a housing with its 174/15 16 R1 359 S coils resting on aspring bracket in contact with the housing so that heat from the coilsis transmitted by [56] References and the bracket to the housing fordissipation thereby.

UNITED STATES PATENTS 1,255,947 2/1918 Thardarson 336/100 X 6 Claims, 4Drawing Figures BALLAST TRANSFORMER WITH HEAT DISSIPATING DEVICE Thepresent invention relates generally to heat dissipating devices and moreparticularly to a heat dissipating device for induction coil devicessuch as ballast transformers of the type used for gaseous discharge lampsystems.

It is an object of the invention to reduce the operating temperatures ofelectrical heat producing devices and particularly induction ballastdevices of the above type.

A particular object of the invention is to provide a simple andinexpensive heat dissipating device for ballast transformers which isreadily assembled with the transformer.

Another particular object of the invention is to directly remove theheat from the coils of transformers of the above type.

Other objects and advantages will become apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention in one of itsaspects relates to an electrical ballast device comprising, incombination, a housing of heat conductive materials having a wall, aninductive ballast device mounted in the housing comprising a core andcoil assembly, a heat conductive resilient member arranged between thecore and coil assembly and the housing wallin thermal contact therewithfor transmitting heat from the assembly to the housing for dissipationthereby, and electrically insulating and thermally conducting meansinterposed between the resilient memher and the core and coil assembly.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing, in which:

FIG. 1 is an elevational view, partly broken away, of an industriallighting fixture having a ballast unit embodying the present invention;

FIG. 2 is a perspective view of the heat transmitting spring bracketincorporated in the FIG. 1 fixture;

FIG. 3 is an enlarged cross-sectional view of the lower portion of theballast unit showing the ballast transformer and spring bracket prior tobeing placed in operative position; and

FIG. 4 is a similar view of the ballast housing showing the ballasttransformer and spring bracket in operative position therein.

Referring now to the drawing, and particularly to FIG. 1, there is showna lighting fixture such as an industrial luminaire for indoor lightingpurposes in which the present invention may typically be embodied. Theillustrated fixture comprises a ballast housing 1 made ofheat-conducting metal, such as aluminum, having a cover 2 and container3 defining an enclosure for housing electrical ballast componentsincluding transformer 4. Suspended from ballast housing I is opticalassembly 5 including reflector 6 in which is mounted lamp 7, such as amercury vapor or other type of gaseous discharge lamp, operated by theballast components in ballast housing I.

As seen in FIGS. 3' and 4, ballast transformer 4 includes a core andcoil assemblly of conventional type comprising a laminated magnetic core8 on which primary coil 9 and secondary coil 10 are wound spaced fromeach other. Typically, coils 9 and 10 are formed .of wire coated withinsulating enamel of conventional type and wound on bobbins 11 and 12 ofelectrically insulating material surrounding core 8. Bobbins l1, 12 haveperipheral flanges or rims for retaining the wire coils, as shown. Aswill be understood, transformer 4 is secured to ballast housing 3 by anysuitable means, not shown, such as by screws engaging the core portions.In-the illustrated arrangement as seen in FIG. 4, the ends oftransformer core 8 rest on steps or ledges 13, 14 formed in ballast'housing 1 as shown, so that in'the assembled condition coils 9 and 10project somewhat into the space between core 8 and bottom wall 3a of theballast housing.

Ballasts of the type described generate a substantial amount of heatduring theoperation of the lighting fixture, and various means have beenemployed in the past for removing the heat from the ballast unit toavoid adverse effects of excessive temperature on the life and operatingcharacteristics of the ballast components and other parts of thefixture. Prior devices employed for this purpose have mainly providedfor thermal contact of the transformercore with a heat sink device orthe outer housing, but such devices have not been fully satisfactorybecause the heat generated by the coil windings has not been adequatelydissipated in this manner. Usually a-larger housing than necessary toenclose the components has been used to dissipate the ballast heat,resulting in a more expensive enclosure.

In accordance with the present invention, a simple and convenient heatremoval device is provided for the ballast unit which directly transfersheat from the coil windings to the ballast housing to markedly reducethe heat level of the ballast component. As seen in FIG. 2, the heatremoval device comprises a spring bracket 15 made of a material of goodheat conductivity, e.g.,

'steel, aluminum, copper or the like, or other stiff spring-likematerial, the bracket having a flat top 15a and being formed at oppositeends with legs or flanges 15b, 15c having a reverse bend or S-shape, sothat the bracket, is resiliently compressible when a load is placed onits upper surface. The free ends of legs 15b,

project a substantial distance laterally beyond the top portion ofbracket 15 when the legs are uncompressed, as seen in FIG. 3. The formand dimensions of bracket 15 are such that it fits readily within thespace or recess at the bottom of ballast housing 1, and when inuncompressed condition, as seen in FIG. 3, has a height somewhat greaterthan the depth of the space left in the final assembly between coils 9,10 and the housing bottom surface on which bracket legs 15b, 15c rest.Also, the overall length of bracket 15 is preferably such that its freeends engage the opposite wall flange portions 30, 3d of ballast housing3 when bracket 15 is uncompressed, i.e., the distance between the freeends of bracket legs 15b, 15c is slightly greater than the distancebetween wall flanges 3c, 3d. Accordingly, when bracket 15 is initiallyplaced in position at the bottom of housing 1, it is frictionallyretained in this position until transformer 4 is placed on its top (seeFIG. 3). As a result of the weight of transformer 4 (or the forceapplied thereby) being exerted on spring bracket 15 in the assembly, thefree ends of bracket 15 are automatically inwardly retracted from thehousing wall flanges to the position shown in FIG. 4.

To ensure effective transmission of heat from coils 9 and 10 to housing3 by way of spring bracket 15 while preventing electrical conductionbetween these parts,

a dielectric sheet'16 of relatively good thermal conductivity isarranged on top of bracket 15 between the latter and coils 9 and 10.Suitable material for this purpose may comprise, for example, a fiberglass sheet or a sheet'of bonded mica flakes, such as a materialcommercially known as mica mat. In addition, a layer 17 of a suitablecomposition or compound that is electrically insulating and thermallyconductive is applied to the outer surface of coils 9, 10 in therecesses defined by the rims of the coil bobbins, so as to fill thespace between the coils and dielectric sheet 16, and is of suchconsistency and resiliency as to have intimate contact with the outerlayer of wire turns of coils 9 and 10 as well as dielectric sheet 16.Such a composition may comprise, for example, a silicone greasecompound. Specific compounds which may be used are polymethyldi-siloxane, phenyl-methyl siloxane, and di-ethyl phenyl siloxane. Ingeneral, any resilient non-flowing material such as high temperaturerubbers or greases having theaforementioned properties may be used. Thecomposition selected for this purpose should not be a solvent for thewire enamel or varnish coating or otherwise adversely affect itsproperties.

By virtue of the described arrangement, heat from the wound coils, whichgenerate a major part of the total heat produced by the transformer, itconducted directly to the metal ballast housing, rather than through thebobbin, core and intervening air gaps such as in conventionalarrangements. Further, since spring bracket is in constant pressurecontact with ballast housing 3 in the assembly, it serves to ensure goodheat transfer between the parts. As a result, the thermal safety marginof ballast and housing combinations is considerably improved, standardtypes of ballast housings may be used with higher watt-loss ballastdesigns than heretofore considered permissible, and less thermallyresistant materials such as used for the insulating wire coating can beemployed with resultant economic savings.

While in the illustrated embodiment spring bracket 15 is arranged at thebottom wall of ballast housing 3, it will be understood that theinvention is not limited to that particular arrangement. Bracket 15 may,for example, be arranged in contact with the top or side walls of theballast housing, depending on the position and configuration of thetransformer and its coils. The specific shape and size of bracket 15may, of course, also be different from that shown without going beyondthe scope of the invention.

In those cases where the rims of bobbins 11 and 12 donot project beyondthe coil surface, the coils 9 and 10 may rest directly on dielectricsheet 16 and resilient layer 17 may be dispensed with. Where no bobbinsare used with the coils and the latter are covered with a dielectrictape, the coils may rest directly on spring bracket 15.

It will be understood that the invention may also have application toheat producing devices other than light fixture ballast components suchas described.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to covoer all such equivalent variations as comewithin the true spirit and scope of the invention.

urged in thermal contact therewith for transmitting heat from saidassembly to said housing for dissipation thereby, and electricallyinsulating and thermally conducting means interposed between saidresilient member and said core and coil assembly, said resilient mem- Iber being formed of a top and compressible spring leg means, saidinductive ballast device resting on said top and holding said spring legmeans compressed in contact with said housing wall, said core and coilassembly comprising an elongated core member and coil means surroundingsaid core member, said coil means resting against said resilient member,said electrically insulating and thermally conducting means beingarranged between said coil means and the top of said resilient member,said electrically insulating and thermally conducting means comprising alayer of elastic material on said coil means and a sheet of dielectricmaterial between said elastic material and said resilient member.

2. An electrical ballast device comprising, in combination, a housing ofheat conductive material having a wall, an inductive ballast devicemounted in said housing comprising a core and coil assembly, a heatconductive resilient member arranged between said core and coil assemblyand said housing wall and resiliently urged in thermal contact therewithfor transmitting heat from said assembly to said housing for dissipationthereby, and electrically insulating and thermally conducting meansinterposed between said resilient member and said core and coilassembly, said resilient member being formed of a top and compressiblespring leg means, said inductive ballast device resting on said top andholding said spring leg means compressed in contact with said housingwall, said core and coil assembly comprising an elongated core memberand coil means surrounding said core member, said coil means restingagainst said resilient member, said electrically insulating andthermally conducting means being arranged between said coil means andthe top of said resilient member said housing having opposite ledges,said elongated core member resting at its opposite ends on said ledgesin thermal contact therewith.

3. An electrical ballast device comprising, in combination, a housing ofheat conductive material having a wall, an inductive ballast devicemounted in said housing comprising a core and coil assembly, a heatconductive resilient member arranged between said core and coil assemblyand said housing wall and resiliently urged in thermal contact therewithfor transmitting heat from said assembly to said housing for dissipationthereby, and electrically insulating and thermally conducting meansinterposed between said resilient member and said core and coilassembly, said heat conductive resilient member comprising a flatbearing portion having spaced legs projecting from one side thereof,.

said legs being of generally S-shaped compressible spring form.

4. A device as defined in claim 3, said housing wall comprising a mainwall portion and opposite flange portions defining a recess forreceiving said resilient member, said spring legs of said resilientmember having free ends projecting laterally in opposite directions, thedistance between said free ends in uncompressed condition of said springlegs beinggreater than the distance between said opposite wall flangeportions, whereby the ends of said spring legs are adapted to engagesaid opposite wall flange portions for holding said resilient member inassembly with said housing when said member is in uncompressedcondition.

5. A device as defined in claim 1, said coil means comprising insulatingbobbin means having a wire coil thereon and spaced rim portionsprojecting beyond said wire coil, said bottom rim portions restingagainst said resilient member and defining therewith a space in whichsaid elastic material is confined.

6. An electrical ballast device comprising, in combination, a housing ofheat conductive material having a wall, an inductive ballast devicemounted in said housing comprising a core and coil assembly, a heatconductive resilient member arranged between said core and coil assemblyand said housing wall and resiliently urged in thermal contact therewithfor transmitting heat from said assembly to said housing for dissipationthereby, and electrically insulating and thermally conducting meansinterposed between said resilient member and said core and coilassembly, said resilient member comprising a flat strip of springmaterial having an intermediate bearing surface and formed at itsopposite ends with generally S-shaped legs having flat bottom portionsgenerally parallel to said intermediate bearing surface and in thermalcontact with said housing wall over substantially their entire bottomsurface.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,883,83 DATED I MAY I3,

INVENTOR(S) CARL M. OSTEEN It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

COL. 1, LINE 26, "MATERIALS" SHOULD BE MATERIAL 3, LINE 26, "IT" SHOULDBE IS 5, LINE 1% "BOTTOM" SHOULD BE BOBBIN Signed and Sealed thistwenty-eight Day Of October 1975 [SEAL] A ttes t:

RUTH C. MASON C. MARSHALL DANN Atlesting Officer (vmmissimrer of Parentsand Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3883,83 I

DATED MAY 1 3, i 75 INVENTOR(S) CARL M, OSTEEN It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

COL. 1, LINE 26, "MATERiALs" SHOULD BE MATERIAL 3, LINE 26, "IT" SHOULDBE is 5, LINE In "BOTTOM" SHOULD BE BOBBIN Bigned and Sealed thistwenty-eight ,D 3y Of October I 975 [S AL] A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oj'larenlsand Trademarks

1. An electrical ballast device comprising, in combination, a housing ofheat conductive material having a wall, an inductive ballast devicemounted in said housing comprising a core and coil assembly, a heatconductive resilient member arranged between said core and coil assemblyand said housing wall and resiliently urged in thermal contact therewithfor transmitting heat from said assembly to said housing for dissipationthereby, and electrically insulating and thermally conducting meansinterposed between said resilient member and said core and coilassembly, said resilient member being formed of a top and compressiblespring leg means, said inductive ballast device resting on said top andholding said spring leg means compressed in contact with said housingwall, said core and coil assembly comprising an elongated core memberand coil means surrounding said core member, said coil means restingagainst said resilient member, said electrically insulating andthermally conducting means being arranged between said coil means andthe top of said resilient member, said electrically insulating andthermally conducting means comprising a layer of elastic material onsaid coil means and a sheet of dielectric material between said elasticmaterial and said resilient member.
 2. An electrical ballast devicecomprising, in combination, a housing of heat conductive material havinga wall, an inductive ballast device mounted in said housing comprising acore and coil assembly, a heat conductive resilient member arrangedbetween said core and coil assembly and said housing wall andresiliently urged in thermal contact therewith for transmitting heatfrom said assembly to said housing for dissipation thereby, andelectrically insulating and thermally conducting means interposedbetween said resilient member and said core and coil assembly, saidresilient member being formed of a top and compressible spring legmeans, said inductive ballast device resting on said top and holdingsaid spring leg means compressed in contact with said housing wall, saidcore and coil assembly comprising an elongated core member and coilmeans surrounding said core member, said coil means resting against saidresilient member, said electrically insulating and thermally conductingmeans being arranged between said coil means and the top of saidresilient member said housing having opposite ledges, said elongatedcore member resting at its opposite ends on said ledges in thermalcontact therewith.
 3. An electrical ballast device comprising, incombination, a housing of heat conductive material having a wall, aninductive ballast device mounted in said housing comprising a core andcoil assembly, a heat conductive resilient member arranged between saidcore and coil assembly and said housing wall and resiliently urged inthermal contact therewith for transmitting heat from said assembly tosaid housing for dissipation thereby, and electrically insulating andthermally conducting means interposed between said resilient member andsaid core and coil assembly, said heat conductive resilient membercomprising a flat bearing portion having spaced legs projecting from oneside thereof, said legs being of generally S-shaped compressible springform.
 4. A device as defined in claim 3, said housing wall comprising amain wall portion and opposite flange portions defining a recess forreceiving said resilient member, said spring legs of said resilientmember having free ends projecting laterally in opposite directions, thedistance between said free ends in uncompressed condition of said springlegs being greater than the distance between said opposite wall flangeportions, whereby the ends of said spring legs are adapted to engagesaid opposite wall flange portions for holding said resilient member inassembly with said housing when said member is in uncompressedcondition.
 5. A device as defined in claim 1, said coil means comprisinginsulating bobbin means having a wire coil thereon and spaced rimportions projecting beyond said wire coil, said bottom rim portionsresting against said resilient member and defining therewith a space inwhich said elastic material is confined.
 6. An electrical ballast devicecomprising, in combination, a housing of heat conductive material havinga wall, an inductive ballast device mounted in said housing comprising acore and coil assembly, a heat conductive resilient member arrangedbetween said core and coil assembly and said housing wall andresiliently urged in thermal contact therewith for transmitting heatfrom said assembly to said housing for dissipation thereby, andelectrically insulating and thermally conducting means interposedbetween said resilient member and said core and coil assembly, saidresilient member comprising a flat strip of spring material having anintermediate bEaring surface and formed at its opposite ends withgenerally S-shaped legs having flat bottom portions generally parallelto said intermediate bearing surface and in thermal contact with saidhousing wall over substantially their entire bottom surface.